Electric discharge lamp mount



March 2, 1954 J. A. sT. Louis Ef AL 2,671,183

ELECTRIC DISCHARGE LAMP MOUNT Filed Sept. l2, 1951 John M POmfrett, bym-'f- 2*/ Their Attorney Patented Mar. 2, 1954 James A. St. Louis, ,Cleveland M'. Pomfrett, illoughby,

Company,A a corporation of General Electric New 'York Heights, and John Dhio, assignors to Application September 12, 195i, SerialNo. 246,268 2 C lams. (Cl. 3155-60) The present invention relates to electric discharge lamps of the high .pressure mercury vapor discharge `type having a vitreous ,aro .tube mounted in a vitreous .outer .envelope and more par- -ticularly the' invention relates to `means for. sup.- porting the arc tube in the outer envelope.

High pressure mercury vapor discharge lamps of the above type have been known commercially for approximately fteen yearsv and are made in 4.09, 250 and l-OO watt sizes at present. Supporting the arc vtube -Within the envelope, particularly in the higher wattage sizes, has presented difficulties heretofore .due to the elevated temperatureof .the tube-duringoperation of the lamp and no completely satisfactorysupport has .been available thoughmany types .have been proposed. Far example, vmetal :support members directly engaging the hot ends kof the .tube led .to electrolysis of .the tube .material which. frequently resulted in cracking Refractory insulating materials, such as mica, having the necessary iiexibility .to .avoid rupturing the tube when .the lamp parts expanded and contracted vduring .service ,frequently became charred .and distorted .in vshape .before Vthe .lamp had reached thelend of vits usefull'ife. further, mica supports give 01T .undesirable .water vapor at the high operating `temperature of the lamp vthus .frequently .caused early .lamp failure.

vThe principal object o f the present Einvention is to provide support means. for the arc tube of high pressure mercury vapor discharge lamps of the above type .which avoids the above .disadvantages. `Another object of .the invention is to provide a high pressure lamp of the abovetype .which has a long useful operating life. Still further objects and advantages .of ,theV invenof the rtube andthe seals.

tion `will be apparent tothoseskilledin the. art A from the following detaileddescription ofspecies thereof and from thev appended'claiins.

In the-drawing accompanyingand formingpart of thisfspecincation a high ,pressuremercury vapor .discharge lamp .havingan arctube. support embodying the present inventionis shown .ina perspective .view as seen Afrom Vabove.

As shown, the lamp comprises a sealed outer envelope -I of glass fha-ving-the usual zscrew type of base ,2 attached ,toone end thereof. Electric leading-inwires .3 ,and .,4 4varev .attached to the threaded shell ...5 and theinsulated center v.ccntact. Siof the base :2,respectivelyand passthrQugh the press Vpart 1 or pinch y1 of Vthe -reentrant -stem tube ,e of the :outer tenveIQpe fl. The .sealed are tube il, .fof :quartz or shardeglass; :conta-.iris- :the usual .fstartingeeas a-imeaeured yernennt -fcf mercury suiicient to produce an unsaturated, high kpressure vapor atmosphere at the operatling temperature of the tube 9.

The tube S is supported within .the outer envelope i by a harness made .up of a substantially U-shaped, stili metal .wire support having connecting its straight legs II and I2 welded to the inner end of said leadingfin wire 3. and a pair of lateral, perforated, thin, plateflike, iiexible metal supports I3 and I4 secured to the legs I i and I 2 of the wire support and engaging the tapered ends of the arc tube e to hold the tube therebetween.

lateral support for the end of the arctubemount. Armetal tie plate il is also attached to and between the free .ends of the legs II .and .I2 to increase the `rigidity of the mount. A heat shield in the form of a perforated metal disc I8 is also attached to the legs I-I and I2 between the stem press fi and the are vtube 9 to protect the glass press stem 'i from excessive heating. lThethree plate-like members I4, II and I8 are Welded .to the legs I I and I2.

The arc tube 9 is provided with a pair Vof main discharge supporting electrodes I9 ,and 2 6 mounted on current rleading-in wires 2| and 22 respectively extending through opposite ends o f the tube 9 and constituting the tube terminals. 'ghe leadin 2i of the upper main electrode Isis connected -to the. current lead textending through the stem press .'I by a flexible conductor 23 pass,- ing through Vthe opening in the heat shield I 8 andisfinsulated from said shield bya glass tube 2t. A flexible conductor 21 y 22 for theopposite main electrode 2t tothe .leg Y,I2 of the U-shape support .which is connected, through lits part It, tothe lead-in wire -3 eX- tending through the stem press l. The main discharge current is supplied to the discharge path between the main electrodes .I9 and 29 by the above described leads and connections.

To facilitate the starting of `the main dis.- charge,an auxiliary starting electrode v2 9 inthe form of a metal wire loop-is'supported.in front of the upper main electrode I9 by the inlefad 3d extending through the upper or startingelectrede end ofthe arc tubes. .When the arctube 9 is of quartz, the inleads St, 2l and .22 are hermetieally united therewith byl glass seal bodies, as is-Well known. Thestarting electrode 2.9 is 4velectrically.connected .to the .lcwermain electrode'tthrouehthe-said inlead-et,thetea! ible conductor 3I attached to one end of a suitable resistor 32 which is supported slightly above the heat shield I8 by the stiff conductor 33 attached to the mid-portion I of the U-shaped mount to which the lower main electrode is electrically connected as described above. The portion of the flexible conductor 3I passing through the opening inthe metal heat shield I8 is electrically insulated therefrom by the glass tube 34.

The auxiliary starting electrode 23 Vis preferably of the type disclosed and claimed in our copending application Serial No. 152,904, iiled March 30, 1950 and assigned to the assignee of the present application, that is, the electrode 29, of tungsten, for example, is of small thermal mass and is mounted in the arc stream between the electrodes I9 and 26 to assume substantially the potential of the adjacent main electrode IS during operation of ythe lamp and thus eliminate electrolysis of the vitreous material between the inleads 3B and I3 of the electrodes 2B and I9, respectively. Of course1 the starting electrode 2e is at the potential of the remote main electrode 20 before the discharge between the main electrode I9 and 20 starts.

In the past, the upper plate-libe support I3 engaging the tapered end of the arc tube 9 has been made of metal and fastened directly to legs II and i2 of the U-shaped support. The said plate-like support was thus charged to the potential of the lower main electrode 2e with the result that current flowed between the plate I3 and the inner elements of the arc tube 9 through the wall of the arc tube causing electrolysis or" l the tube material with consequent weakening and eventual .break down of this portion of the tube wall before full operating life of the lamp had been attained. The electrolysis and eventual break down took place not only at the parts of the tube engaged by the support but also at the glass seals between the inleads and the tube. Attempts to solve the problem by using an electrically insulating support of similar shape instead of a metal support I3 for the end of the arc tube were not completely satisfactory because the otherwise suitable material, mica, charred and warped under the high temperature to which it was subjected during operation of the lamp to end the life of the lamp prematurely by failing to properly support 4the arc tube 9 in the outer envelope I. Also, as stated above, mica supports gave oi water vapor during operation of the lamp and thus caused lamp failures.

The novel structure of the lamp of the present invention completely avoids the prior diiculties by using a metal plate support I3 and by charging the said metal plate support to the same potential as the upper main electrode I9 and the auxiliary electrode 29 during operation of the lamp. The metal plate I3 does not give off water vapor, is not subject to charring and warping as is a mica plate, for example, and the charge of equal potential on the plate I3 and on the upper electrodes I9 and 29 avoids electrolysis of the arc tube material and the glass seals. The useful operating life oi the lamp is thus increased substantially.

To impress a suitable charge on the metal support plate I3 the plate is electrically connected by the exible conductor to the conductor 23 of the upper main electrode I9 and is electrically insulated from both legs II and I2 of the U-shaped support by a pair of insulating ferrules 36 of steatite for example, having ilanges 31 4 around the legs II and I2 and passing through openings in the ends of the support I3. The flanges 3l on the ferrules 36 are held down against the top surface of the support plate I3 by metal pieces 38 on the legs yI I and I2 to hold the arc tube 9 between the support plates I3 and It.

The sides 35 of the opening in the supports I3 and I4 are slightly rounded in cross section as shown at the broken portion of support I3, to avoid presenting ya sharp edge to the end of the arc tube 9 while retaining a line contact between the tube 9 and the supports i3 and I4. A sharp metal edge engaging the arc tube B is not desirable because it frequently digs into the tube and weakens it, but a line contact obtained with such an edge is desirable because it minimizes the transfer of heat from the tube 9 to the supports I3 and I4. The rounded edge 39 of the supports I3 and I4 thus avoids the undesirable feature of a sharp edge but retains the advantages thereof.

W h at we claim as new and desire to secure by Letters Patent of the United States is:

l. An electric discharge lamp comprising in combination, an electric discharge tube of vitreous material having main discharge supporting electrodes mounted on electric terminals sealed into and extending from its ends and a starting electrode mounted on an inlead extending through one end of the tube and supported thereby in the discharge path between said main electrodes and adjacent the main electrode at the said tube end, an enclosing vitreous envelope therefor having current inleads sealed therein at one end thereof and means within said envelope to support said tube, said means comprising a substantially U-shaped metal wire support and a pair of transverse metal supports mounted on the legs of said U-shaped support and engaging opposite ends of said tube, the electric terminal at the end of said tube remote from said starting electrode being connected to one of said inleads through said U-shaped support and the electric terminal at the starting electrode end of said tube being connected to another of said inleads through a conductor electrically insulated from said U-shaped support, the transverse metal support engaging the starting electrode end of said tube being electrically insulated from said U-shaped support and being electrically connected to the terminal at said end and said starting electrode being of small thermal mass so as to assume substantially the potential of the adjacent main electrode during operation of the discharge whereby said transverse support, said starting electrode and the adjacent main electrode are at the same potential during operation of the lamp and electrolysis of the arc tube material at the starting electrode end of the tube is minimized, said transverse supports having openings to receive the ends of said arc tube, said arc tube ends being tapered and the sides of the openings in said supports being rounded whereby a line contact with no sharp edges is established between said tube ends and said supports.

2. An electric discharge lamp comprising in combination, a sealed electric discharge tube of vitreous material having main discharge supporting electrodes mounted on electric terminals at its ends and a starting electrode mounted on an inlead extending through one end of the tube and supported thereby in the discharge path between said main electrodes and adjacent the main electrode at the said tube end. an enclosing vitreous envelope for said tube having current inleads Sealed therein at one end thereof and means within said envelope to support said tube, said means comprising a substantially U-shaped and a pair of transverse metal on the legs of said U-shaped support and engaging opposite ends of said tube, the electric terminal at the end of said tube remote from said starting electrode being connected to one of said envelope inleads through said U-shaped support, the electric terminal at the starting electrode end of said tube being connected to another of said envelope inleads through a conductor electrically insulated from said U-shaped support, the inlead for said starting electrode being connected through a resistance to said U-shaped support, the transverse JAMES A. ST. LOUIS. JOHN M. POMFRETT. 

